The structure-function relationships of the anti-tumor lectins ricin and abrin will be investigated by locating regions of amino acid sequence homology and correlating these with the biological activity of fragments containing these regions. The sequences of abrin A chain and abrin and ricin B chains and peptides derived by chemical and enzymatic cleavages will be determined by automatic Edman degradation. The established primary structures and the published data for ricin A chain will be examined for regions of sequence homology and compared with data from three dimensional structural studies. Fragments of the chains generated in the sequence work and peptides prepared to encompass the homology regions will be tested for biological activity. A chain fragment will be tested for the ability to inhibit protein synthesis by a cell free translation system while B chain fragments will be tested for ability to bind to cells. Correlation of the data on biological activity with the amino acid sequence should help establish a structural basis for the design of chemotherapeutic agents with anti-tumor activity.